One method of manufacturing ophthalmic lenses, such as intraocular lenses and contact lenses, is by cast molding.
Cast molding of contact lenses is well known. See, for example, Appleton, et al., U.S. Pat. No. 5,466,147, Morris, U.S. Pat. No. 6,405,993, and Dean, U.S. Pat. No. 6,732,993.
Typically, a single mold assembly for molding a single contact lens product includes a female mold section having a concave optical surface defining an anterior surface of a lens to be made, and a male mold section having a convex optical surface defining a posterior surface of the lens to be made. Thus when the male and female mold sections are assembled together, a contact lens shaped cavity is formed between the concave surface of the female section and the convex surface of the male section.
The female and male mold sections are commonly produced by injection molding techniques. A common method of forming a lens mold section is to utilize metal tooling insert, which has typically been machine lathed to define a desired contact lens surface, to form the molding surface of the mold section.
A process for cast molding a lens is as follows. A polymerizable lens material, for example, a monomeric material or other lens precursor material is placed on a concave surface of a contact lens mold section. This is usually done by manually withdrawing the lens precursor material from a large volume container containing the precursor material with an Eppendorf tube and dispensing a volume of the precursor material onto a mold or mold section. Typically, a person would fill the Eppendorf tube with the material and dispense between about 30 μL and about 50 μL onto the concave surface of the mold section. This method is labor intensive, presents substantial risks to people handling the precursor material, and can result in increased waste of the precursor material since large volumes of the material remain in the jar for extended periods of time, which can degrade or deteriorate over time.
Once filled, a second mold section is placed on top of the first mold section to form a lens shaped cavity containing the lens precursor material. The contact lens precursor material is cured for example, by applying heat and/or light or other suitable polymerizing means to the filled mold assembly, thereby producing a contact lens product or contact lens between the mold sections. The contact lens product is then removed from the mold sections. The mold sections are often destroyed during this removal step. The contact lens product is often an unfinished contact lens which is subjected to one or more finishing steps, for example, conventional finishing steps such as hydration, to produce the final contact lens.
One obstacle associated with cast molding processes is the appropriate placement and fixation of the mold sections, particularly after the lens precursor material has been placed between the mold sections and prior to polymerization thereof. For example, it may be difficult to secure two mold sections together to form a mold assembly without opacification, pitting, or bubble formation in the lens cup (e.g., the region of the mold section containing the lens precursor material). Further, it may also be difficult to form a mold assembly in which the lens precursor material has a substantially uniform thickness, or in other words the lens does not have an undesired prism due to thickening of the lens precursor material at one region of the lens cup relative to another different region.
In addition, because of the potentially fragile nature of the polymerized contact lens product, the mold sections should be separable without causing breakage of or damage to the lens product.
A variety of traditional methods are used in a non-automated production laboratory setting for placing one mold section upon another and then securing the two sections in a relatively fixed position such as by weighting or clamping. While this may be a somewhat acceptable practice on a small scale production basis, it may not satisfy all of the requirements of large scale and/or automated high speed manufacturing production of contact lenses.
Directed energy techniques, such as ultrasonic welding are known in the art for permanently joining materials such as polymers without consideration for later separation.
Galas, U.S. Pat. No. 5,759,318, describes an apparatus and method that includes the use of ultrasonic energy for releasably fixing assembled sections of a lens molding assembly using a ultrasonically produced annulus of fusion completely circumscribing the contact lens forming material contained between the assembled sections.
More effective, more reliable methods and systems for manufacturing lenses, for example filling and coupling mold sections during manufacturing of contact lenses, are needed.